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. 2019 Mar-Apr;24(2):142-150.
doi: 10.1016/j.rpor.2019.01.001. Epub 2019 Jan 22.

Local control rates in stereotactic body radiotherapy (SBRT) of lung metastases associated with the biologically effective dose

Daniel Zucca Aparicio  1 , Ovidio Hernando Requejo  2 , Miguel Ángel de la Casa de Julián  1 , Carmen Rubio Rodríguez  2 , Pedro Fernández Letón  1
Affiliations

Local control rates in stereotactic body radiotherapy (SBRT) of lung metastases associated with the biologically effective dose

Daniel Zucca Aparicio et al. Rep Pract Oncol Radiother. 2019 Mar-Apr.

Abstract

Aim: To evaluate dose differences in lung metastases treated with stereotactic body radiotherapy (SBRT), and the correlation with local control, regarding the dose algorithm, target volume and tissue density.

Background: Several studies showed excellent local control rates in SBRT for lung metastases, with different fractionation schemes depending on the tumour location or size. These results depend on the dose distributions received by the lesions in terms of the tissue heterogeneity corrections performed by the dose algorithms.

Materials and methods: Forty-seven lung metastases treated with SBRT, using intrafraction control and respiratory gating with internal fiducial markers as surrogates (ExacTrac, BrainLAB AG), were calculated using Pencil Beam (PB) and Monte Carlo (MC) (iPlan, BrainLAB AG).Dose differences between both algorithms were obtained for the dose received by 99% (D 99%) and 50% (D 50%) of the planning treatment volume (PTV). The biologically effective dose delivered to 99% (BED99%) and 50% (BED50%) of the PTV were estimated from the MC results. Local control was evaluated after 24 months of median follow-up (range: 3-52 months).

Results: The greatest variations (40.0% in ΔD 99% and 38.4% in ΔD 50%) were found for the lower volume and density cases. The BED99% and BED50% were strongly correlated with observed local control rates: 100% and 61.5% for BED99% > 85 Gy and <85 Gy (p < 0.0001), respectively, and 100% and 58.3% for BED50% > 100 Gy and <100 Gy (p < 0.0001), respectively.

Conclusions: Lung metastases treated with SBRT, with delivered BED99% > 85 Gy and BED50% > 100 Gy, present better local control rates than those treated with lower BED values (p = 0.001).

Keywords: Biologically effective dose; Local control; Lung metastases; SBRT.

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Figures

Fig. 1
Fig. 1
Dose–volume deviations between Monte Carlo (DMC) and Pencil Beam (DPB), normalized to the prescription dose (Dp), received by 99% and 50% of the planning target volume (PTV), ΔD99% and ΔD50% respectively, regarding: (a) the inverse value of the target volume and (b) the average electron density.
Fig. 2
Fig. 2
Temporal evolution of the biologically effective dose (BED), and the averaged value (horizontal lines), received by 99% and 50% of the PTV. The use of the MC dose algorithm on 2011 is shown as a gap. BED99% PB and BED50% PB are the BED recalculated with MC for the plans originally calculated and delivered with the PB algorithm, while BED99% MC and BED50% MC represent the BED for the plans actually calculated and delivered with the MC dose distribution.
Fig. 3
Fig. 3
Tumour control probabilities (TCP) found for the BED received by 99% and 50% of the PTV, BED99% and BED50% respectively. Dashed and solid lines represent the TCP models that best fit to the achieved results.
Fig. 4
Fig. 4
Local control rates found for (a) the BED received by 99% and (b) 50% of the PTV. BED99% > 85 Gy and BED50% > 100 Gy are correlated to better local control rates than those treated with lower BED values (p = 0.001).
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